The rubber composition of the tread is a major determinant of the running properties of a tire, in particular of a pneumatic tire. The rubber mixtures used in drive belts and other belts, and in hoses, especially in the locations exposed to high mechanical loads, are likewise substantially responsible for the stability and durability of these rubber items. These rubber mixtures for pneumatic tires, drive belts and other belts, and hoses are therefore subject to very stringent requirements.
An important constituent of rubber mixtures is elemental sulfur, which during the vulcanization process is essential for the crosslinking of the polymers present in the rubber mixture. Inadequate and/or poor crosslinking is reflected in defective physical properties of the rubber mixture. If the sulfur is to be capable of ensuring good crosslinking, it must be well dispersed in the rubber mixture, that is, uniformly distributed.
The sulfur used in pneumatic tires and in technical rubber products is often an insoluble sulfur, to which oil is admixed in order to prevent dusting and thus to prevent explosions during production or processing. This oil generally involves plasticizer oils of the type commonly used in the rubber industry, for example naphthenic oils.
The oil used determines to a not inconsiderable extent the dispersibility of the sulfur.